Margriet Kwint

Intra anatomical changes during radiotherapy 75 4 ◀ Figure 1: Four examples of the traffic light protocol. left: planning CT (pCT), right: cone beam CT (CBCT). Purple: planning target volume (PTV); Red: gross tumor volume (GTV). First row: example of level red change; this patient had cT4N2M0 NSCLC and was treated with 24x 2.75 Gy. This is the CBCT of week 3, the atelectasis resolved and this resulted in a tumor shift outside PTV. Second row: example of level orange change; this patient had cT4N2M0 NSCLC and was treated with 24x 2.75 Gy. In week 1 the CBCT showed development of atelectasis without a tumor shift. Third row: example level yellow change; this patient had cT4N2M0 NSCLC and was treated with 17x 3Gy. This CBCT shows regression in week 3 of the treatment. Fourth row: example level green, no change. Recurrence, the patient was treated with 17x 3Gy. The image is the CBCT of fraction 15. Intra Thoracic Anatomical Changes All CBCT’s were added to a database. All CBCT’s were scored retrospectively and compared to the planning-CT (bony anatomy, carina, trachea and mediastinal contour were used to compare the CBCT with the planning-CT). Two IGRT-specialists independent of each other visually evaluated every CBCT. For each CBCT, the observed ITACs were scored: changes in atelectasis, infiltrative changes, pleural effusion, considerable tumor baseline shift, tumor regression and tumor progression. If an ITAC was detected, the date of the first occurrence of the highest level (red, orange, yellow or green) of each ITAC was compiled. Furthermore, subsequent actions, e.g. a repeat radiotherapy planning-CT-scan or re-planning were scored. Statistical analysis To evaluate the ITACs during the course of radiotherapy SPSS for windows software, version 20, was used for statistical analysis. Firstly, descriptive statistics were used to analyze the number of ITACs. Thereafter Spearman’s rank correlation coefficients were used to analyze if there were any significant correlations between progression and an adaptive treatment plan with the following parameters: tumor regression, tumor baseline shift, changes in atelectasis, pleural effusion, infiltrative changes, traffic light level of changes, changes in the first week, patient characteristics, tumor stage, tumor location, type of treatment and time interval between planning-CT and first day of treatment.